Gas separation membranes with intermixed layers

ABSTRACT

A composite membrane comprising:
     a) a porous support;   b) a gutter layer; and   c) a discriminating layer;
 
wherein at least 10% of the discriminating layer is intermixed with the gutter layer.

RELATED APPLICATION DATA

This application is a continuation application which claims priority toU.S. patent application Ser. No. 14/409,559, filed on Dec. 19, 2014,which is a National Stage Application under 35 U.S.C. 371 of co-pendingPCT application PCT/GB2013/051685 designating the United States andfiled Jun. 26, 2013; which claims the benefit of GB application1211309.8 and filed Jun. 26, 2012 each of which are hereby incorporatedby reference in their entireties.

This invention relates to composite membranes and to their preparationand use for the separation of gases.

Composite gas separation membranes are known from U.S. Pat. No.5,286,280 ('280). The '280 membranes comprise, in order, a support, agas-permeable polymeric layer (often referred to as a “gutter layer”), adiscriminating layer and optionally an outer protective layer. '280mentions that the solvents used to form the discriminating layer mustnot attack the gutter layer, hence the discriminating layer of '280 willnot permeate into the gutter layer.

There is a need for robust membranes in which the layers have a lowtendency to separate, which can operate at high pressures with good gasflux and good discrimination between gases such as CO₂ and CH₄.

According to a first aspect of the present invention there is provided acomposite membrane comprising:

-   a) a porous support;-   b) a gutter layer; and-   c) a discriminating layer;    wherein at least 10% of the discriminating layer is intermixed with    the gutter layer.

FIGS. 1 and 2 schematically illustrate composite membranes according tothe invention.

The composite membrane illustrated schematically in FIGS. 1 and 2comprises a porous support 1, a gutter layer 2 and a thin discriminatinglayer 3.

In FIG. 1, the portion of the discriminating layer 3 which is notintermixed with the gutter layer is indicated as 3 a and the portion ofthe discriminating layer which is intermixed with the gutter layer isindicated as 3 b. In FIG. 1, DL_(e) and DL_(i) respectively indicate thethicknesses of the non-intermixed and intermixed portions of thediscriminating layer. As DL_(e) and DL_(i) are about equal in FIG. 1,about 50% of the discriminating layer is intermixed with the gutterlayer.

In FIG. 2, 100% of the discriminating layer 3 is completely intermixedwith the gutter layer 2.

In FIGS. 1 and 2, the relative thicknesses of porous support 1, gutterlayer 2 and a discriminating layer 3 are not to scale relative to eachother and have been exaggerated to illustrate the invention moreclearly. In particular, the discriminating layer 3 is usually very thincompared to the gutter layer 2, but in these drawings we haveexaggerated the relative thickness of the discriminating layer relativeto the gutter layer to more clearly illustrate the invention.

Also the composite membranes illustrated in FIGS. 1 and 2, optionallyfurther comprises a protective layer on the discriminating layer (notshown).

In the composite membranes of the invention, the gutter anddiscriminating layer are adhered together very strongly due to theabovementioned intermixing. As a result, the composite membranes arerobust and discriminating layer has a very low tendency to peel awayfrom the gutter layer in use, even when the membranes are used at highgas pressures.

The primary purpose of the porous support is to provide mechanicalstrength to the composite membrane without materially reducing the flux.Therefore the porous support is typically open pored, relative to thediscriminating layer.

The porous support may be, for example, a microporous organic orinorganic membrane, or a woven or non-woven fabric.

The porous support may be constructed from any suitable material.Examples of such materials include polysulfones, polyethersulfones,polyimides, polyetherimides, polyamides, polyamideimides,polyacrylonitrile, polycarbonates, polyesters, polyacrylates, celluloseacetate, polyethylene, polypropylene, polyvinylidenefluoride,polytetrafluoroethylene, poly(4-methyl 1-pentene) and especiallypolyacrylonitrile.

One may use, for example, a commercially available, porous sheetmaterial as the support. Alternatively one may prepare the poroussupport using techniques generally known in the art for the preparationof microporous materials. In one embodiment one may prepare a porous,non-discriminatory support by curing curable components, then applyingfurther curable components to the formed porous support and curing suchcomponents thereby forming the gutter layer and the discriminating layeron the already cured porous support.

The porous support is not limited to sheet form; also porous supports intubular form can be used.

One may also use a porous support which has been subjected to a coronadischarge treatment, glow discharge treatment, flame treatment,ultraviolet light irradiation treatment or the like, e.g. for thepurpose of improving its wettability and/or adhesiveness.

The porous support preferably possesses pores which are as large aspossible, consistent with providing a smooth surface for the gutterlayer and subsequent discriminating layer. The porous support preferablyhas an average pore size of at least about 50% greater than the averagepore size of the discriminating layer, more preferably at least about100% greater, especially at least about 200% greater, particularly atleast about 1000% greater than the average pore size of thediscriminating layer.

The pores passing through the porous support typically have an averagediameter of 0.001 to 10 μm, preferably 0.01 to 1 μm. The pores at thesurface of the porous support will typically have a diameter of 0.001 to0.1 μm, preferably 0.005 to 0.05 μm.

The pore diameter may be determined by, for example, viewing the surfaceof the porous support by scanning electron microscopy (“SEM”) or bycutting through the support and measuring the diameter of the poreswithin the porous support, again by SEM.

The porosity at the surface of the porous support may also be expressedas a % porosity, i.e.

${\%\mspace{14mu}{porosity}} = {100\% \times \frac{( {{area}\mspace{14mu}{of}\mspace{14mu}{the}\mspace{14mu}{surface}\mspace{14mu}{which}\mspace{14mu}{is}\mspace{14mu}{missing}\mspace{14mu}{due}\mspace{14mu}{to}\mspace{14mu}{pores}} )}{( {{total}\mspace{14mu}{surface}\mspace{14mu}{area}} )}}$

The areas required for the above calculation may be determined byinspecting the surface of the porous support using a SEM.

Thus, in a preferred embodiment, the porous support has a %porosity >1%, more preferably >3%, especially >10%, more especially>20%.

The porosity of the porous support may also be expressed as a CO₂ gaspermeance (units are m³ (STP)/m²·s·kPa). When the composite membrane isintended for use in gas separation the porous support preferably has aCO₂ gas permeance of 5 to 150×10⁻⁵ m³ (STP)/m²·s·kPa, more preferably of5 to 100, most preferably of 7 to 70×10⁻⁵ m³ (STP)/m²·s·kPa.

Alternatively the porosity is characterised by measuring the N₂ gas flowrate through the porous support. Gas flow rate can be determined by anysuitable technique, for example using a Porolux™ 1000 device, availablefrom porometer.com.

Typically the Porolux™ 1000 is set at the maximum pressure (about 34bar) and one measures the flow rate (L/min) of N₂ gas through the poroussupport under test. The N₂ flow rate through the porous support at apressure of about 34 bar for an effective sample area of 2.69 cm²(effective diameter of 18.5 mm) is preferably >1 L/min, morepreferably >5 L/min, especially >10 L/min, more especially >25 L/min.

The higher of these flow rates are preferred because this reduces thelikelihood of the gas flux of the resultant composite membrane beingreduced by the porous support.

The abovementioned % porosity and permeance refer to the porous supportused to make the composite membrane (i.e. before the gutter layer andany other layers have been applied thereto).

The porous support preferably has an average thickness of 20 to 500 μm,preferably 50 to 400 μm, especially 100 to 300 μm.

One may use an ultrafiltration membrane as the porous support, e.g. apolysulfone ultrafiltration membrane, cellulosic ultrafiltrationmembrane, polytetrafluoroethylene ultrafiltration membrane,polyvinylidenefluoride ultrafiltration membrane and especiallypolyacrylonitrile ultrafiltration membrane.

Asymmetric ultrafiltration membranes may also be used, including thosecomprising a porous polymer membrane (preferably of thickness 10 to 150μm, more preferably 20 to 100 μm) and optionally a woven or non-wovenfabric support. The porous support is preferably as thin as possible,provided it retains the desired structural strength.

In one embodiment the gutter layer is present on the porous support anddoes not permeate into the support to any significant extent. However ina preferred embodiment a portion of the gutter layer is present withinthe support and a portion of the gutter layer is outside of the supportand the following conditions are satisfied:

-   (i) the portion of the gutter layer outside of the support has an    average thickness (GL_(e)) of 10 nm to 900 nm; and-   (ii) the portion of the gutter layer present within the support has    an average thickness (GL_(i)) of 10% to 350% of GL_(e).

The portion of the gutter layer outside of the support preferably has anaverage thickness (GL_(e)) of 200 to 900 nm, more preferably 400 to 900.

The portion of the gutter layer present within the support preferablyhas an average thickness of 10% to 200% of GL_(e), more preferably 20%to 90% of GL_(e).

The thicknesses GL_(e) and GL_(i) may be determined by cutting throughthe composite membrane and examining its cross section by SEM. Bymeasuring the thickness of layers at several locations using a SEM onemay calculate the average thickness.

In cases where it is difficult to determine where the various layersbegin and end by SEM, one may instead use time-of-flight secondary ionmass spectrometry (ToF-SIMS) depth profiling. For example, when thediscriminating layer diffuses into the gutter layer in a graduatedmanner, the point at which the gutter layer finishes may not be clearlydefined and it may therefore be difficult to measure DL_(i). In suchcases, the point at which the discriminating layer is deemed to finishis the point at which the concentration of the discriminating layer inthe gutter layer drops to 20%. The point at which the concentration ofthe discriminating layer in the gutter layer drops to 20% may bedetermined by ToF-SIMS depth profiling, for example using the conditionsdescribed in the Examples. In ToF-SIMS depth profiling, an ion gun isoperated in the DC mode during the sputtering phase in order to removematerial from the composite membrane surface, and the same ion gun or asecond ion gun is operated in the pulsed mode for an acquisition phase.Depth profiling by ToF-SIMS allows monitoring of all species of interestsimultaneously, and with high mass resolution and clearly shows theextent to which the discriminating layer intermixes with the gutterlayer due to the change in chemical composition at that point.Similarly, ToF-SIMS depth profiling clearly shows the junction betweenthe gutter layer and the porous support due to their very differentchemical compositions. For gutter layers rich in silicon-containingcompounds, the change in silicon content is a very good marker for thebeginning and end of the gutter layer, even when the gutter layer has aheterogenous chemical composition due to different permeation rates ofits precursor components. Also the beginning and end of thediscriminating layer may similarly be determined. In discriminatinglayers containing fluorine or acetyl-groups, a significant fall in thefluorine content or acetyl-group content (as measured by ToF-SIMS depthprofiling) indicates the end of the discriminating layer.

One may control the extent to which the discriminating layer isintermixed with the gutter layer by any of a number of techniques. Forexample, one may apply the discriminating layer to the gutter layer inthe form of a solution comprising a solvent which partially dissolves orswells the gutter layer. In this way, the components which ultimatelyform the discriminating layer can permeate into the gutter layer toprovide a region where the discriminating layer is intermixed with thegutter layer. By varying the amount of inert solvent and good solventfor the gutter layer, one may also vary the extent to which thediscriminating layer intermixes with the gutter layer.

Similarly, when the composition used to form the discriminating layer iscurable, one may control the extent to which the discriminating layer isintermixed with the gutter layer by controlling the amount of time thecomposition is in contact with the gutter layer before it is cured, e.g.by irradiation. When the composition is cured shortly after it has beenapplied to the gutter layer, the extent of intermixing is less than whenthe composition is cured after a longer time period in contact with thegutter layer.

A particularly good solvent non-solvent pair for controlling the extentto which the discriminating layer is intermixed with the gutter layer ismethyl ethyl ketone (MEK) and tetrahydrofuran (THF). For many gutterlayers, increasing the proportion of THF increases the % intermixing,while increasing the proportion of MEK decreases the % intermixing. Bycontrolling the ratio of MEK:THF in the composition used to form thediscriminating layer one may therefore also control the extent to whichthe discriminating layer is intermixed with the gutter layer from 10 and100%.

The % of the discriminating layer which is intermixed with the gutterlayer is preferably the volume % (vol %). As illustrated in FIG. 1, theaverage thicknesses of the portion of the discriminating layer which isnot intermixed with the gutter layer may be referred to as DL_(e). Theaverage thicknesses of the portion of the discriminating layer which isintermixed with the gutter layer may be referred to as DL_(i). Thereforeone may determine the (vol.) % of the discriminating layer which isintermixed with the gutter layer by measuring DL_(i) and DL_(e) andperforming the calculation [DL_(i)/(DL_(e)+DL_(i))]×100%. Thus when thethickness DL_(i) is 10% of the total thickness of the discriminatinglayer (DL_(e)+DL_(i)), then 10% of the discriminating layer isintermixed with the gutter layer. When DL_(e) is 0 and DL_(i) is >0,100% of the discriminating layer is intermixed with the gutter layer.

One may control the extent to which the gutter layer permeates into thesupport (i.e. the ratio of GL_(i):GL_(e)) by any of a number oftechniques. For example, when the gutter layer is obtained by curing acurable composition, one may appropriately select a curable compositionviscosity and time delay between applying this composition to the poroussupport and curing. By varying the viscosity and/or time delay, one mayalso vary the % of the gutter layer which is present within the poroussupport (e.g. to ensure it is 10 to 350%).

One may control the overall thickness of the gutter layer(GL_(i)+GL_(e)) by controlling the solids content and amount of curablecomposition applied to the porous support per unit area.

In order to reduce the value of GL_(i), one may partially fill the poresof the porous support with an inert liquid before applying aradiation-curable composition to the porous support. This inert liquidis not radiation-curable and prevents the radiation-curable liquid whichforms the gutter layer from permeating too far into the porous supportand thereby ensures the desired proportion of gutter layer is within theporous support. Preferably the inert liquid is immiscible with theradiation-curable composition used to form the gutter layer. Thistechnique has an advantage over the first technique mentioned above inthat one may form thinner membranes and more application techniques areavailable for lower viscosity, radiation-curable compositions.

Another option for ensuring that the curable composition does notpermeate excessively into the porous support (i.e. to keep the value ofGL_(i) low) is to increase the hydrodynamic radius (Rhyd) of aradiation-curable polymer used to form the gutter layer. Rhyd may beincreased by increasing the extent to which the radiation-curablepolymer is crosslinked. Rhyd can be suitably determined by dynamic lightscattering.

In one embodiment, the radiation-curable composition used to form thegutter layer comprises a partially crosslinked, radiation-curablepolymer (“PCP Polymer”), preferably having a Rhyd of more than half theaverage diameter of at least 50% of the pores at the surface of theporous support.

The PCP Polymer may be obtained by partially curing a compositioncomprising one or more curable components (e.g. monomers, oligomersand/or polymers), at least one of which comprises a dialkylsiloxanegroup. Preferably the partial cure is performed by a thermally initiatedpolymerisation process.

In a preferred embodiment, at least one of the curable componentscomprises a group which is both thermally curable and radiation curable.This is because one may then use a thermally initiated process forpreparing the PCP Polymer and subsequently use a radiation initiatedprocess for forming the gutter layer on the porous support.Alternatively, the thermally curable group and the radiation curablegroups are different groups and are part of the same component used tofrom the PCP Polymer.

As thermal curing is a relatively slow process, one may partially curethe curable components thermally to form the PCP Polymer, then stop orslow down the thermal cure process, then apply a composition containingthe PCP Polymer to the support in the form of a composition comprisingan inert solvent, and then irradiate the composition on the support toform the gutter layer. The thermal cure process may be stopped or sloweddown simply by cooling (e.g. to below 30° C.) and/or diluting thecomposition and/or removing the catalyst if present used to make the PCPPolymer at an appropriate time.

Groups which are curable both thermally and by irradiation include epoxygroups and ethylenically unsaturated groups such as (meth)acrylicgroups, e.g. (meth)acrylate groups and (meth)acrylamide groups.

Typically the components used to form the PCP Polymer are selected suchthat they are reactive with each other. For example, a component havingan epoxy group is reactive with a component comprising, for example, anamine, alkoxide, thiol or carboxylic acid group. One or more of thecomponents used to form the PCP Polymer may also have more than onecurable group. Components having an ethylenically unsaturated group maybe reacted with other components by a free radical mechanism or,alternatively, with a nucleophilic component having for example one ormore thiol or amine groups.

The PCP Polymer is preferably obtained by thermally curing a compositioncomprising:

-   (i) a component which is both thermally curable and radiation    curable and which comprises one or more dialkoxysilane groups;-   (ii) a crosslinking agent which is copolymerisable with    component (i) when heated; and-   (iii) inert solvent; and optionally-   (iv) a catalyst.

The term “comprising” as used in this specification is to be interpretedas specifying the presence of the stated parts, steps or components, butdoes not exclude the presence of one or more additional parts, steps orcomponents.

Reference to an element by the indefinite article “a” or “an” in thisspecification does not exclude the possibility that more than one of theelement(s) is present, unless the context clearly requires that there beone and only one of the elements. The indefinite article “a” or “an”thus usually means “at least one”.

Preferably the amount of inert solvent present in the composition isfrom 5 to 95 wt %, more preferably 10 to 80 wt %, especially 30 to 70 wt%.

Component (i) preferably comprises at least 3 radiation-curable groupsper molecule.

The alkyl groups in the dialkylsiloxane groups are preferably eachindependently C₁₋₄-alkyl groups, especially methyl groups.

Preferably component (i) is free from phenyl siloxane groups (e.g. offormula —(Si(Ph)₂-O)— groups wherein Ph is a phenyl or phenylene group.

Component (i) preferably has a number average molecular weight (“NAMW”),of 1 to 500 kDa, preferably 1 to 100 kDa, especially 2 to 50 kDa. TheNAMW may be determined by any technique known in the art such as dynamiclight scattering or size exclusion chromatography.

Component (i) is preferably present in an amount of 1 to 95 wt %, morepreferably 5 to 75, especially 10 to 50 wt %, relative to the weight ofthe composition used to make the PCP Polymer.

As examples of component (i) there may be mentioned polydimethylsiloxaneepoxy (meth)acrylates, polydimethylsiloxane (meth)acrylates, and allylmodified, vinyl modified, (meth)acrylic modified, epoxy-modifiedpolydimethylsiloxanes and mixtures comprising two or more thereof.

Component (i) may also comprise several different radiation-curablecomponents comprising one or more dialkoxysilane groups components.

Component (i) also comprises one or more thermally curable groups. Thisis necessary so that component (i) can cure thermally to provide the PCPPolymer.

Examples of crosslinking agents which may be used as component (ii)include: polydimethylsiloxane comprising two or more reactive groups,for example two or more groups selected from carboxylic acid, hydroxyl,thiol and/or anhydride groups, preferably polydimethylsiloxane having atleast two of such groups (e.g. at both ends); (cyclo)aliphatic oraromatic di-, tri- or poly-carboxylic acids, e.g. succinic acid,glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid,1,2-benzenedicarboxylic acid, 1,3-benzenedicarboxylic acid,1,4-benzenedicarboxylic acid, trimesic acid; (cyclo)aliphatic oraromatic di-, tri- or poly-thiols, e.g. 1,2-ethanedithiol,1,4-butanedithiol, 1,6-hexanedithiol, benzene-1,2-dithiol,benzene-1,3-dithiol, benzene-1,4-dithiol, 1,2-benzenedimethanethiol,1,3-benzenedimethanethiol, 1,4-benzenedimethanethiol ortoluene-3,4-dithiol; (cyclo)aliphatic or aromatic di-, tri- orpoly-amines, e.g. ethylenediamine, 1,2-diaminopropane,1,3-diaminopropane, 1,4-diaminobutane, cadaverine, hexamethylenediamine,1,8-diaminooctane, 1,2-bis(3-aminopropylamino)ethane,1,2-diaminocyclohexane, 4-aminobenzylamine, o-xylylenediamine,o-phenylenediamine, m-phenylenediamine, p-phenylenediamine; or(cyclo)aliphatic or aromatic anhydrides, e.g. succinic anhydride,3,3-dimethylglutaric anhydride, ethylenediaminetetraacetic dianhydride,glutaric anhydride, phenylsuccinic anhydride, pyromellitic dianhydride,or phthalic anhydride; metal alkoxides, e.g. alkoxides of zirconium,titanium or niobium, especially titanium (IV) isopropoxide, titanium(IV) ethoxide, zirconium propoxide and/or niobium ethoxide. Preferablythe crosslinking agent comprises two (i.e. two and not more than two)reactive groups.

When component (ii) is or comprises a metal complex it may also serve asthe metal complex mentioned in the first aspect of the presentinvention.

The function of the inert solvent (iii) is to provide the compositionused to make the PCP Polymer with a concentration suitable for thethermal crosslinking reaction to proceed efficiently and/or to controlthe viscosity of the composition. Typically the inert solvent used ascomponent (iii) comprises one or more organic solvents, especiallywater-immiscible organic solvent(s). The inert solvent is referred to as“inert” because it is not curable.

As examples of inert solvents there may be mentioned: C₅-C₁₀(cyclo)alkanes, benzene, alkylbenzenes (e.g. toluene), C₃-C₁₀(optionally branched) ketones, C₄-C₁₀ cyclic ketones, C₄-C₁₀ (optionallybranched) esters, C₄-C₁₀ cyclic esters, C₄-C₁₀ (optionally branched)ethers, C₄-C₁₀ cyclic ethers and especially n-heptane and n-octane.Preferably the inert solvent comprises one or more, especially from 1 to8, of the abovementioned preferred inert solvents.

Suitable catalysts (iv) include, for example, amine, phosphonium andmetal compounds, e.g. amines such as 2-ethylhexylamine,bis(2-ethylhexyl)amine, dodecyldimethylamine, n,n-dimethylbenzylamine,2-ethylimidazole, 1,8-diazabicyclo[5.4.0]undec-7-ene, tetramethylguanidine, tetrabutylammonium chloride, benzyltrimethyl ammoniumbromide, benzyltrimethyl ammonium hydroxide, tetrabutyl ammoniumhydroxide, crosslinked polyvinylpyridine, and polymer bound amines suchas polymer bound 1,4-diazabicyclo[2.2.2]octane hydrochloride, polymerbound 1,8-diazabicyclo[5.4.0] undec-7-ene and polymer boundtetraalkylammonium carbonate; phosphonium compounds such as tetrabutylphosphonium bromide, pentyltriphenylphosphonium bromide, polymer boundtriphenylphosphonium chloride; metal compounds such as titanium (iv)isopropoxide, diisopropoxytitanium-bis-(acetylacetonate), titanium (iv)2-ethylhexyloxide, titanium (iv) butoxide, titanium butylphosphate,zirconium (iv) propoxide, zirconium (iv) ethoxide, zirconium (iv)acetylacetonate, zirconium (iv) bis(diethyl citrato)-dipropoxide,niobium ethoxide, aluminum acetylacetonate, aluminum lactate, bismuthoctoate, calcium octoate, cerium naphthenate, chromium (iii)2-ethylhexanoate, cobalt octoate, copper (ii) acetylacetonate, iron(iii) acetylacetonate, magnesium 2,4-pentadionate, manganesenaphthenate, nickel acetylacetonate, stannous octoate, titanium ethylacetoacetate chelate, titanium acetylacetonate chelate, titaniumtriethanolamine chelate, zinc acetate, zinc acetylacetonate, zincdi-2-ethylhexyldithio-phosphate, zinc nitrate, zinc octoate, zirconium6-methylhexanedione, zirconium octoate, zirconium (iv)trifluoroacetylacetone, and the like. Catalysts generally are used inconcentrations ranging from about 0.004 to about 1 wt %, preferably fromabout 0.01 to about 0.5 wt %, relative to the total weight of curablecomponents.

The radiation-curable composition which may be used to form the gutterlayer preferably comprises:

-   (1) 0.5 to 50 wt % of a PCP Polymer;-   (2) 0 to 5 wt % of a photo-initiator; and-   (3) 50 to 99.5 wt % of inert solvent.

In order for the PCP Polymer to be radiation-curable, it has at leastone radiation-curable group. Radiation curable groups includeethylenically unsaturated groups (e.g. (meth)acrylic groups (e.g.CH₂═CRC(O)— groups), especially (meth)acrylate groups (e.g. CH₂═CRC(O)O— groups), (meth)acrylamide groups (e.g. CH₂═CR C(O)NR— groups),wherein each R independently is H or CH₃) and especially epoxide groups(e.g. glycidyl and epoxycyclohexyl groups). Preferably the PCP Polymercomprises epoxide groups because such groups do not suffer from cureinhibition due to the presence of oxygen. The PCP polymers have a highaffinity for oxygen and this oxygen can sometimes inhibit the curing ofother curable groups.

The preferred ethylenically unsaturated groups are acrylate groupsbecause of their fast polymerisation rates, especially when theirradiation uses UV light. Many compounds having acrylate groups arealso easily available from commercial sources.

Photo-initiators may be included in the curable composition and areusually required when curing uses UV radiation. Suitablephoto-initiators are those known in the art such as radical type, cationtype or anion type photo-initiators.

Cationic photo-initiators are preferred when the PCP Polymer comprisescurable groups such as epoxy, oxetane, other ring-opening heterocyclicgroups or vinyl ether groups.

Preferred cationic photo-initiators include organic salts ofnon-nucleophilic anions, e.g. hexafluoroarsinate anion, antimony (V)hexafluoride anion, phosphorus hexafluoride anion and tetrafluoroborateanion. Commercially available cationic photo-initiators includeUV-9380c, UV-9390c (manufactured by Momentive performance materials),UVI-6974, UVI-6970, UVI-6990 (manufactured by Union Carbide Corp.),CD-1010, CD-1011, CD-1012 (manufactured by Sartomer Corp.),Adekaoptomer™ SP-150, SP-151, SP-170, SP-171 (manufactured by AsahiDenka Kogyo Co., Ltd.), Irgacure™ 250, Irgacure™ 261 (Ciba SpecialtyChemicals Corp.), CI-2481, CI-2624, CI-2639, CI-2064 (Nippon Soda Co.,Ltd.), DTS-102, DTS-103, NAT-103, NDS-103, TPS-103, MDS-103, MPI-103 andBBI-103 (Midori Chemical Co., Ltd.). The above mentioned cationicphoto-initiators can be used either individually or in combination oftwo or more.

Radical Type I and/or type II photo-initiators may also be used.

Examples of radical type I photo-initiators are as described in WO2007/018425, page 14, line 23 to page 15, line 26, which areincorporated herein by reference thereto.

Examples of radical type II photo-initiators are as described in WO2007/018425, page 15, line 27 to page 16, line 27, which areincorporated herein by reference thereto.

Preferably the weight ratio of photo-initiator to radiation-curablecomponents present in the radiation-curable composition is between 0.001and 0.2 to 1, more preferably between 0.01 and 0.1 to 1. A single typeof photo-initiator may be used but also a combination of severaldifferent types.

When no photo-initiator is included in the radiation-curablecomposition, the composition can be advantageously cured byelectron-beam exposure. Preferably the electron beam output is between50 and 300 keV. Curing can also be achieved by plasma or coronaexposure.

The function of the inert solvent (3) is to provide theradiation-curable composition with a viscosity suitable for theparticular method used to apply the curable composition to the poroussupport. For high speed application processes one will usually choose aninert solvent of low viscosity. The number of parts of component (3) ispreferably 70 to 99.5 wt %, more preferably 80 to 99 wt %, especially 90to 98 wt %.

In a specific embodiment there is no solvent present.

In some instances, the individual components within the curablecomposition used to make the gutter layer may permeate into the poroussupports at different rates. Therefore it is possible for the chemicalcomposition of the gutter layer to be heterogeneous, e.g. with theportion of the gutter layer which is present within the support having adifferent chemical composition to the portion of the gutter layer whichis outside of the support, due to these differences in permeation rates.It will be understood, therefore, that the present invention includeswithin its scope composite membranes, as defined above, where the gutterlayer is homogenous or heterogenous.

Conveniently the composite membranes of the present invention may beprepared by a process comprising the steps of applying aradiation-curable composition to a porous support, preferably using amultilayer coating method (e.g. a consecutive multilayer coatingmethod), optionally allowing the radiation-curable composition topermeate into the support, irradiating the radiation-curable compositionto form a gutter layer, applying to the gutter layer a composition usedto form the discriminating layer on the gutter layer and allowing atleast 10% of the composition to permeate into the gutter layer.

In a preferred consecutive multilayer process a layer of theradiation-curable composition and the discriminating layer (or thechemicals used to prepare the discriminating layer) are appliedconsecutively to the porous support, with the radiation-curablecomposition being applied before the discriminating layer.

In order to produce a sufficiently flowable composition for use in ahigh speed coating machine, the radiation-curable composition preferablyhas a viscosity below 4000 mPa·s when measured at 25° C., morepreferably from 0.4 to 1000 mPa·s when measured at 25° C. Mostpreferably the viscosity of the radiation-curable composition is from0.4 to 500 mPa·s when measured at 25° C. For coating methods such asslide bead coating the preferred viscosity is from 1 to 100 mPa·s whenmeasured at 25° C. The desired viscosity is preferably achieved bycontrolling the amount of solvent in the radiation-curable compositionand/or by the conditions for preparing the radiation curable polymer.

In the multi-layer coating methods mentioned above one may optionally beused to apply a lower inert solvent layer to the porous support followedby applying the radiation-curable composition.

With suitable coating techniques, coating speeds of at least 5 m/min,e.g. at least 10 m/min or even higher, such as 15 m/min, 20 m/min, oreven up to 100 m/min, can be reached. In a preferred embodiment theradiation-curable composition is applied to the support at one of theaforementioned coating speeds.

The thickness of the gutter layer on the support may be influenced bycontrolling the amount of curable composition per unit area applied tothe support. For example, as the amount of curable composition per unitarea increases, so does the thickness of the resultant gutter layer. Thesame principle applies to formation of the discriminating layer and theoptional protective layer.

While it is possible to practice the invention on a batch basis with astationary porous support, to gain full advantage of the invention it ismuch preferred to perform the process on a continuous basis using amoving porous support, e.g. the porous support may be in the form of aroll which is unwound continuously or the porous support may rest on acontinuously driven belt. Using such techniques the radiation-curablecomposition can be applied to the porous support on a continuous basisor it can be applied on a large batch basis. Removal of the inertsolvent from the radiation-curable composition membrane can beaccomplished at any stage after the radiation-curable composition hasbeen applied to the support, e.g. by evaporation.

Thus in a preferred process, the radiation-curable composition isapplied continuously to the porous support by means of a manufacturingunit comprising a radiation-curable composition application station, thecomposition is cured using an irradiation source located downstream fromthe radiation-curable composition application station, thediscriminating layer is formed on the gutter layer by a discriminatinglayer application station and the resultant composite membrane iscollected at a collecting station, wherein the manufacturing unitcomprises a means for moving the porous support from theradiation-curable composition application station to the irradiationsource and to the discriminating layer application station and to thecomposite membrane collecting station.

In one embodiment the discriminating layer is formed on the gutter layerby a radiation curing process. Under such circumstances, themanufacturing unit preferably further comprises an irradiation source ora heater located downstream from the discriminating layer applicationstation, thereby radiation- or thermally-curing the components used toform the discriminating layer.

The radiation-curable composition application station may be located atan upstream position relative to the irradiation source and theirradiation source is located at an upstream position relative to thediscriminating layer application station.

The gutter layer usually has the function of providing a smooth andcontinuous surface for the discriminating layer. While it is preferredfor the gutter layer to be pore-free, the presence of some pores usuallydoes not reduce the permselectivity of the final membrane because thediscriminating layer is often able to fill minor defects in the gutterlayer.

Preferably the gutter layer comprises dialkylsiloxane groups, especiallydimethylsiloxane groups.

The gutter layer is preferably essentially nonporous, i.e. any porespresent therein have an average diameter <1 nm. This does not excludethe presence of defects which may be significantly larger. Defects maybe corrected by the discriminating layer as described above.

The irradiation step may be performed using any source which providesthe wavelength and intensity of radiation necessary to cause theradiation-curable composition to polymerise.

For example, electron beam, UV, visible and/or infra red radiation maybe used to cure the composition, the appropriate radiation beingselected to match the composition. For UV curing a mercury arc lamp isparticularly effective, but light emitting diodes can also be used.

Preferably radiation curing of the radiation-curable composition beginswithin 7 seconds, more preferably within 5 seconds, most preferablywithin 3 seconds, of the radiation-curable composition being applied tothe porous support.

Preferably the curing is achieved by irradiating the radiation-curablecomposition for less than 30 seconds, more preferably less than 10seconds, e.g. less than 5 seconds.

The radiation-curable composition is preferably irradiated withultraviolet light or an electron beam.

Preferably the irradiation uses ultraviolet light. Suitable wavelengthsare for instance UV-A (400 to >320 nm), UV-B (320 to >280 nm), UV-C (280to 200 nm), provided the wavelength matches with the absorbingwavelength of any photo-initiator included in the composition.

Suitable sources of ultraviolet light include mercury arc lamps, carbonarc lamps, low pressure mercury lamps, medium pressure mercury lamps,high pressure mercury lamps, swirlflow plasma arc lamps, metal halidelamps, xenon lamps, tungsten lamps, halogen lamps, lasers andultraviolet light emitting diodes. Particularly preferred areultraviolet light emitting lamps of the medium or high pressure mercuryvapour type. In addition, additives such as metal halides may be presentto modify the emission spectrum of the lamp. In most cases lamps withemission maxima between 200 and 450 nm are particularly suitable.

The energy output of the irradiation source is preferably from 20 to1000 W/cm, preferably from 40 to 500 W/cm but may be higher or lower aslong as the desired exposure dose can be realized.

The discriminating layer preferably has pores of average diameter below2 nm, preferably below 1 nm, and preferably is substantially non-porous.Preferably the discriminating layer has a very low permeability toliquids.

The discriminating layer preferably has an average thickness of 10 to400 nm, more preferably 10 to 300 nm, especially 20 to 100 nm.

The average thickness may be determined by cutting through the compositemembrane and measuring the thickness of the discriminating layer aboveand within the gutter layer in several places using a scanning electronmicroscope and calculating the average. Preferably, however, thethickness measurements are performed by Tof-SIMS depth profiling asdescribed above.

Preferably the gutter layer contains a metal and Si (silicon) in a molarratio of at least 0.0005, especially in a ratio of about 0.008:1.

The composition used to make the discriminating layer preferablycomprises a polymer, an inert solvent and optionally an initiator. Theinert solvent may be any solvent capable of dissolving the polymer usedto form the discriminating layer. Suitability of the solvent isdetermined by the properties of the polymer and the concentrationdesired. Suitable solvents include water, C₅₋₁₀ alkanes, e.g.cyclohexane, heptane and/or octane; alkylbenzenes, e.g. toluene, xyleneand/or C₁₀₋₁₆ alkylbenzenes; C₁₋₆ alkanols, e.g. methanol, ethanol,n-propanol, isopropanol, n butanol, sec-butanol, tert-butanol,n-pentanol, cyclopentanol and/or cyclohexanol; linear amides, e.g.dimethylformamide or dimethylacetamide; ketones and ketone-alcohols,e.g. acetone, methyl ether ketone, methyl isobutyl ketone, cyclohexanoneand/or diacetone alcohol; ethers, e.g. tetrahydrofuran and/or dioxane;diols, preferably diols having from 2 to 12 carbon atoms, e.g.pentane-1,5-diol, ethylene glycol, propylene glycol, butylene glycol,pentylene glycol, hexylene glycol and/or thiodiglycol; oligo- andpoly-alkyleneglycols, e.g. diethylene glycol, triethylene glycol,polyethylene glycol and/or polypropylene glycol; triols, e.g. glyceroland/or 1,2,6 hexanetriol; mono-C₁₋₄-alkyl ethers of diols, preferablymono-C₁₋₄-alkyl ethers of diols having 2 to 12 carbon atoms, e.g.2-methoxyethanol, 2-(2-methoxyethoxy)ethanol, 2-(2ethoxyethoxy)-ethanol, 2-[2-(2-methoxyethoxy)ethoxy]ethanol,2-[2-(2-ethoxyethoxy)-ethoxy]-ethanol and/or ethyleneglycolmonoallylether; cyclic amides, e.g. 2-pyrrolidone,N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, caprolactam and/or1,3-dimethylimidazolidone; cyclic esters, e.g. caprolactone;sulphoxides, e.g. dimethyl sulphoxide and/or sulpholane; and mixturescomprising two or more of the foregoing, particularly a mixturecomprising methyl ethyl ketone and tetrahydrofuran.

The discriminating layer preferably comprises a polyimide, celluloseacetate, polyethyleneoxide or polyetherimide, especially a polyimidecomprising trifluoromethyl groups. A particularly preferreddiscriminating layer comprises a polyimide comprising groups of theFormula (1):

Polyimides comprising trifluoromethyl groups may be prepared by, forexample, the general methods described in U.S. Pat. No. Reissue 30,351(based on U.S. Pat. No. 3,899,309), U.S. Pat. No. 4,717,394 and U.S.Pat. No. 5,085,676.

When the discriminating layer is cured after applying it to the gutterlayer the composition used to prepare the discriminating layerpreferably comprises an initiator, preferably a thermal initiator or aphotoinitiator. The initiator may be selected from those described abovefor the gutter layer.

The discriminating layer may be formed on the gutter layer by anysuitable technique, for example by a process comprising any of thecoating methods described above in relation to preparation of the gutterlayer.

For improving the adhesion of the discriminating layer onto the gutterlayer, the latter may be treated by a corona discharge or plasmatreatment before forming the discriminating layer thereon. For thecorona or plasma treatment generally an energy dose of 0.5 to 100 kJ/m²is preferred.

The optional protective layer may be formed on the discriminating layerby any suitable technique, for example by a process comprising any ofthe coating methods described above in relation to preparation of thegutter layer.

The protective layer, when present, preferably is highly permeable tothe gases or vapours that are to be separated. Preferably the protectivelayer comprises dialkylsiloxane groups.

The protective layer optionally has surface characteristics whichinfluence the functioning of the composite membrane, for example bymaking the membrane surface more hydrophilic.

The composite membrane preferably has a pure water permeability at 20°C. of less than 6.10⁻⁸ m³/m²·s·kPa, more preferably less than 3.10⁻⁸m³/m²·s·kPa.

The overall dry thickness of the composite membrane will typically be 20to 500 μm, preferably from 30 to 300 μm.

In one embodiment, the gutter layer is applied to the porous support bymeniscus type dip coating of a radiation-curable composition onto theporous support and the discriminating layer (or the components fromwhich the discriminating layer is derived) is applied to the gutterlayer by reverse kiss gravure coating, meniscus type dip coating orpre-metered slot die coating. Alternatively the radiation-curablecomposition may be applied to the support by pre-metered slot diecoating or multi roll gravure coating. The radiation-curable compositionand the discriminating layer may also be applied by curtain coating ifdesired.

For production of a composite membrane on a small scale, it isconvenient to apply all of the layers (i.e. the gutter layer,discriminating layer and protective layer (when present)) by reversekiss gravure coating, forward kiss gravure coating, meniscus type dipcoating, pre-metered slot die coating or spin coating. A three-rolloffset gravure coating may also be used, especially when thecompositions to be applied to the support etc. have relatively highviscosity.

The process for making the composite membrane may contain further stepsif desired, for example washing and/or drying one or more of the variouslayers and removing the inert solvent from the composite membrane, e.g.by evaporation.

The composite membrane is preferably in tubular or, more preferably, insheet form. Tubular forms of membrane are sometimes referred to as beingof the hollow fibre type. Membranes in sheet form are suitable for usein, for example, spiral-wound, plate-and-frame and envelope cartridges.

The composite membranes are particularly suitable for separating a feedgas containing a target gas into a gas stream rich in the target gas anda gas stream depleted in the target gas.

For example, a feed gas comprising polar and non-polar gases may beseparated into a gas stream rich in polar gases and a gas streamdepleted in polar gases. In many cases the membranes have a highpermeability to polar gases, e.g. CO₂, H₂S, NH₃, SO_(x), and nitrogenoxides, especially NO_(x), relative to non-polar gases, e.g. alkanes,H₂, and N₂.

The target gas may be, for example, a gas which has value to the user ofthe composite membrane and which the user wishes to collect.Alternatively the target gas may be an undesirable gas, e.g. a pollutantor ‘greenhouse gas’, which the user wishes to separate from a gas streamin order to protect the environment.

The composite membranes are particularly useful for purifying naturalgas (a mixture which comprises methane) by removing polar gases (CO₂,H₂S); for purifying synthesis gas; and for removing CO₂ from hydrogenand from flue gases. Flue gases typically arise from fireplaces, ovens,furnaces, boilers, combustion engines and power plants. The compositionof flue gases depend on what is being burned, but usually they containmostly nitrogen (typically more than two-thirds) derived from air,carbon dioxide (CO₂) derived from combustion and water vapour as well asoxygen. Flue gases also contain a small percentage of pollutants such asparticulate matter, carbon monoxide, nitrogen oxides and sulphur oxides.Recently the separation and capture of CO₂ has attracted attention inrelation to environmental issues (global warming).

The composite membranes of the invention are particularly useful forseparating the following: a feed gas comprising CO₂ and N₂ into a gasstream richer in CO₂ than the feed gas and a gas stream poorer in CO₂than the feed gas; a feed gas comprising CO₂ and CH₄ into a gas streamricher in CO₂ than the feed gas and a gas stream poorer in CO₂ than thefeed gas; a feed gas comprising CO₂ and H₂ into a gas stream richer inCO₂ than the feed gas and a gas stream poorer in CO₂ than the feed gas,a feed gas comprising H₂S and CH₄ into a gas stream richer in H₂S thanthe feed gas and a gas stream poorer in H₂S than the feed gas; and afeed gas comprising H₂S and H₂ into a gas stream richer in H₂S than thefeed gas and a gas stream poorer in H₂S than the feed gas.

Preferably the composite membrane has a CO₂/CH₄ selectivity (αCO₂/CH₄)>20. Preferably the selectivity is determined by a processcomprising exposing the membrane to a 13:87 mixture by volume of CO₂ andCH₄ at a feed pressure of 6000 kPa and a temperature of 40° C.

Preferably the composite membrane has a CO₂/N₂ selectivity (αCO₂/N₂)>35. Preferably the selectivity is determined by a processcomprising exposing the membrane to CO₂ and N₂ separately at feedpressures of 2000 kPa and a temperature of 40° C.

While this specification emphasises the usefulness of the compositemembranes of the present invention for separating gases, especiallypolar and non-polar gases, it will be understood that the compositemembranes can also be used for other purposes, for example providing areducing gas for the direct reduction of iron ore in the steelproduction industry, dehydration of organic solvents (e.g. ethanoldehydration), pervaporation and vapour separation and also forbreathable apparel. The composite membranes of the present invention areparticularly useful for refining methane from biogas, e.g. using amembrane/absorption hybrid method in conjunction with an absorptionsolution, for example, as described in JP-A-2007-297605.

According to a further aspect of the present invention there is provideda gas separation module comprising a composite membrane according to thefirst aspect of the present invention.

The module may take any convenient form, for example include spiral,hollow, pleat, tubular, plate and frame modules etc. are preferred.

The composite membranes of the present invention exhibit good flux andseparation selectivity. They can endure bending and have a low tendencyto form undesirable pin holes. The membranes are stable under a varietyof conditions, including hot and humid conditions.

The invention is now illustrated by the following non-limiting examplesin which all parts and percentages are by weight unless otherwisespecified. (“Ex.” means Example. “CEx.” means Comparative Example. GLmeans gutter layer, DL means discriminating layer and PL meansprotective layer).

The following materials were used in the Examples:

-   PAN is a polyacrylonitrile L10 ultrafiltration membrane from GMT    Membrantechnik GmbH, Germany (a porous support).-   X-22-162C is crosslinking agent (a dual end reactive silicone having    carboxylic acid reactive groups, a viscosity of 220 mm 2/s and a    reactive group equivalent weight of 2,300 g/mol) from Shin-Etsu    Chemical Co., Ltd. (MWT 4,600).

-   DBU is 1,8-diazabicyclo[5.4.0]undec-7-ene from Sigma Aldrich.-   UV9300 is SilForce™ UV9300 from Momentive Performance Materials    Holdings. This is thermally curable copolymer comprising reactive    epoxy groups and linear polydimethyl siloxane chains. Furthermore,    this copolymer cures rapidly when irradiated with UV light in the    presence of a photo-initiator.

-   I0591 4-isopropyl-4′-methyldiphenyliodonium    tetrakis(pentafluorophenyl) borate (C₄₀H₁₈BF₂₀I) from Tokyo Chemical    Industries N.V. (Belgium):

-   Ti(OiPr)₄ is titanium (IV) isopropoxide from Dorf Ketal Chemicals    (MWT 284).-   n-heptane is n-heptane from Brenntag Nederland BV.-   MEK is 2-butanone from Brenntag Nederland BV.-   MIBK is methylisobutyl ketone from Brenntag Nederland BV.-   APTMS is 3-trimethoxysilyl propan-1-amine from Sigma Aldrich.-   THF is tetrahydrofuran from Brenntag Nederland BV.-   PI1 is 6FDA-TeMPD x/DABA y, x/y=20/80; obtained from Fujifilm    Corporation, having the following structure:

poly([(R{2,3,5,6-tetramethyl-1,4-phenylenediamine}-alt-{5,5′-[2,2,2-trifluoro-1-(trifluoromethyl)ethane-1,1-diyl]bis(isobenzofuran-1,3-dione)})-co-[{5-carboxylic-1,3-phenylenediamine}-alt-{5,5′-[2,2,2-trifluoro-1-(trifluoromethyl)ethane-1,1-diyl]bis(isobenzofuran-1,3-dione)}])obtained from Fujifilm Corporation.

-   PI2 is    poly([({2,3,5,6-tetramethyl-1,4-phenylenediamine}-alt-{5,5′-[2,2,2-trifluoro-1-(trifluoromethyl)ethane-1,1-diyl]bis(isobenzofuran-1,3-dione)})-co-[{1,3-phenylenediamine}-alt-{5,5′-[2,2,2-trifluoro-1-(trifluoromethyl)ethane-1,1-diyl]bis(isobenzofuran-1,3-dione)}]-co-[{5-(2-methacryloyloxy)ethoxycarbonyl-1,3-phenylenediamine}-alt-{5,5′-[2,2,2-trifluoro-1-(trifluoromethyl)ethane-1,1-diyl]bis(isobenzofuran-1,3-dione)}])    wherein the ratio of the 2,3,5,6-tetramethyl-1,4-phenylenediamine    group, the 1,3-phenylenediamine group and the 5-(2-methacryloyloxy)    ethoxycarbonyl-1,3-phenylenediamine group is 40:50:10, obtained from    Fujifilm Corporation.-   CA is cellulose acetate CA-398-3 from Eastman Chemicals.-   AC is acetone from Brenntag Nederland BV.-   PS783 is (84% by weight) dimethyl siloxane, (16% by weight)    diphenylsiloxane; vinyl terminated, from UCT inc.-   PC072 is platinum divinyl complex containing 2-3% platinum by weight    from UCT inc.-   PS123 is trimethylsilyl terminated methylhydro, dimethylsiloxane    copolymer having 30-35% weight % of methylhydro groups, from UCT    inc.

All materials were used without further purification.

(A) Measurement of Layer Thicknesses by ToF-SIMS Depth Profiling

The layer thicknesses, including the discriminating layer, DL_(e) andDL_(i), were measured by ToF-SIMS depth profiling using a Ulvac-PHITRIFT V nano TOF surface analysis instrument. The following conditionswere used:

-   -   Ulvac-PHI TRIFT V nano TOF,    -   Bi₃ ⁺⁺ primary ion (30 kV, DC 4 nA),    -   Ar-GCIB Ar₂₅₀₀ ⁺, 15 kV, 1 nA for depth profile analysis.        (B) Adhesion

The strength of the adhesion between the layers of the compositemembranes was measured using the method according of JIS-K5600. Afteraging for 16 hours at 25 degrees celsius and 60% RH, the surface of thecomposite membranes under test were cut using a multiple blade cutter (6blades) at 2 mm spacing. The sticky side of an adhesive tape (77 mm inlength) was applied to the cut surface and the tape was then pulled off.The cut surface was then examined visually/using a microscope to assessthe extent to which the layer(s) were removed from the compositemembrane. The membranes were then given a score as follows:

-   -   OK—the surface remained intact    -   M—the surface was only moderately damaged    -   NOK—the adhesive tape removed the surface layer(s)        Preparation of Radiation-Curable Polymers PCP1 and PCP2

The components UV9300, X-22-162C and DBU were dissolved in n-heptane inthe amounts indicated in Table 1 and maintained at a temperature of 95°C. for 168 hours to give partially cured polymer PCP1. PCP1 had an Sicontent (meq/g polymer) of 12.2 and the resultant n-heptane solution ofPCP1 had a viscosity of 22.8 mPas at 25.0° C. PCP2 was 100% UV9300.

TABLE 1 Ingredients used to Prepare PCP1: PCP1 Ingredient Amount (w/w %)UV9300 (w/w %) 39.078 X-22-162C (w/w %) 10.789 DBU (w/w %) 0.007n-Heptane (w/w %) 50.126PCP2 was Prepared as Follows:

The catalyst PC072 was diluted to a 10% solution by weight in acetone. Amixture of PS783 (a siloxane, 4.0 g), PS123 (a crosslinking agent, 0.10g), acetone (12.0 g) and the diluted PC072 solution (0.11 g, 10% byweight PC072) was placed in a capped test tube and kept in an oven at61° C. for four hours, with periodic manual tumbling at approximately 20minute intervals.

Preparation of the Curable Compositions G1 and G2

To make curable composition G1, the solution of PCP1 arising from theprevious step above was cooled to 20° C. and diluted using n-heptane togive the PCP1 concentration indicated in Table 2 below. The solution wasthen filtered through a filter paper having a pore size of 2.7 μm. Thephotoinitiator I0591 and a metal complex (Ti(OiPr)₄) were then added tothe filtrate in the amounts indicated in Table 2 to give curablecomposition G1. The amount of Ti(OiPr)₄ present in G1 corresponded to105.6 μmol of Ti(OiPr)₄ per gram of PCP1. Also the molar ratio ofmetal:silicon in G1 was 0.0087.

To make curable composition G2 the resultant solution of PCP2 polymerwas then poured into a cup containing acetone (83.684 g) to dilute thepre-cured PS783 to a 4% solution by weight (4.0 g in 100 g totalsolution). A second aliquot of PS123 (0.10 g) was then added to the 100g solution to facilitate post-curing.

Curable compositions G1 and G2 had the formulations shown in Table 2below:

TABLE 2 Preparation of Curable Composition G1 and G2 Amount (w/w %)Ingredient G1 G2 PCP1 polymer concentration in curable 5.0 — composition(w/w %) PCP2 Polymer concentration in curable — 4.0 composition (w/w %)PS123 — 0.1 I0591 0.1 — Ti(OiPr)₄  0.15 —

The above % for G2 in Table 2 relate to the concentration of therelevant component in the acetone.

Curable compositions G1 and G2 were used to prepare the gutter layerand/or the protective layer, as described in more detail below.

Step a) Formation of the Gutter Layer

Two porous support+gutter layer composites, PSG1 and PSG2, were preparedas described below:

Preparation of the Porous Support+Gutter Layer Composite PSG1

Curable composition G1 was applied to a PAN (a porous support) by spincoating and subsequently cured using a Light Hammer LH10 from Fusion UVSystems fitted with a D-bulb with an intensity of 24 kW/m and dried. Theaverage gutter layer thickness was determined by cutting through thePAN+gutter layer composite and measuring the thickness in several placesfrom the surface of the PAN support outwards by SEM and calculating theaverage. The average gutter layer of thickness was found to be 400 nm.

Preparation of the Porous Support+Gutter Layer Composite PSG2

Curable composition G2 was applied to PAN (a porous support) by meniscuscoating process at 10 m/min. The solvents were allowed to evaporate inambient air and the composite was post-cured in an oven of about 60degree Celsius for 2 hours to completely cure the siloxane. The averagegutter layer thickness was determined by cutting through the PAN+gutterlayer composite and measuring the thickness in several places from thesurface of the PAN support outwards by SEM and calculating the average.The average gutter layer of thickness was found to be 1000 nm.

Step b) Formation of the Discriminating Layer

Compositions D1 to D9 used to prepare the discriminating layers wereprepared by mixing the ingredients indicated in Table 3:

TABLE 3 Ingredient D1 D2 D3 D4 D5 D6 D7 D8 D9 PI1 1.5 1.5 1.5 1.5 1.51.5 — — 1.0 PI2 — — — — — — — 1.5 — CA — — — — — — 1.5 — — APTMS 0.0150.015 0.015 0.015 0.015 — — 0.015 — MIBK 4.50 4.50 4.50 4.50 4.50 4.504.50 4.50 — THF 7.485 17.485 27.485 37.485 47.485 7.500 7.485 7.485 —MEK 86.50 76.50 66.50 56.50 46.50 86.50 86.50 86.50 — AC — — — — — — — —99.0

The compositions D1 to D9 were each independently applied to theporous-support+gutter layer composites indicated in Table 4 below byspin coating. A series of composite membranes were thereby preparedhaving a variety of discriminating layer thicknesses and % intermixingwith the gutter layers.

For each composite membrane described in Table 4, ToF-SIMS depthprofiling was used to measure (i) the average thicknesses of the portionof the discriminating layer which was not intermixed with the gutterlayer (DL_(e); (ii) the average thicknesses of the portion of thediscriminating layer which was intermixed with the gutter layer(DL_(i)); and (iii) the average total thickness of the discriminatinglayer (DL_(t)) The total discriminating layer thicknessDL_(t)=DL_(i)+DL_(e). The % of the discriminating layer intermixed withthe gutter layer was calculated by the equation[DL_(i)/(DL_(i)+DL_(e))×100%] and the results are shown in Table 4.

Step c) Formation of the Protective Layer

The radiation-curable composition G1 described in Table 2 was applied byspin coating to the PAN+gutter layer+discriminating layer compositemembranes indicated in Table 4 arising from step b). The composition G1was cured thereon using a Light Hammer LH10 from Fusion UV Systemsfitted with a D-bulb with an intensity of 24 kW/m and dried.

The protective layer thickness was measured by cutting through thecomposite membrane and measuring the thickness of the outermost layerfrom the surface of the discriminating layer by SEM. In the exampleswhich contained a protective layer, the thickness of the protectivelayer was found to be 600 nm.

Results

The adhesion properties of the resultant composite membranes aredescribed in Table 4 below:

TABLE 4 Composite Membrane Components PS + GL DL PL DL_(e) DL_(i) %intermix Adhesion Ex. 1 PSG1 D1 G1 75 15 17 OK Ex. 2 PSG1 D1 G1 352 4812 OK Ex. 3 PSG1 D1 G1 27 13 33 OK Ex. 4 PSG1 D2 G1 70 20 22 OK Ex. 5PSG1 D3 G1 66 24 27 OK Ex. 6 PSG1 D4 G1 48 42 47 OK Ex. 7 PSG1 D5 G1 3258 64 OK Ex. 8 PSG1 D6 G1 79 11 12 M Ex. 9 PSG1 D7 G1 70 20 22 OK Ex. 10PSG2 D1 G1 79 11 12 OK Ex. 11 PSG1 D8 G1 77 13 14 M Ex12 PSG1 D1 — 75 1517 OK Ex13 PSG1 D7 — 70 20 22 OK Cex1 PSG1 D9 G1 90 0 0 NOK Note: InTable 4, “PSG” refers to the porous support + gutter layer compositeused to make the composite membrane. D1 to D9 refer to the compositionsused to make the discriminating layer. G1 refers to the curablecomposition used to make the protective layer, when present. DL_(e) andDL_(i) were measured by ToF-SIMS depth profiling,

The invention claimed is:
 1. A composite membrane comprising: a) aporous support; b) a gutter layer; and c) a discriminating layer;wherein the discriminating layer comprises a polyimide, celluloseacetate, polyethyleneoxide or polyetherimide and wherein at least 10% ofthe discriminating layer is intermixed with the gutter layer.
 2. Thecomposite membrane according to claim 1 wherein the discriminating layerhas an average thickness of 10 to 400 nm.
 3. The composite membraneaccording to claim 1, wherein the discriminating layer comprises apolyimide comprising trifluoromethyl groups.
 4. The composite membraneaccording to claim 1, wherein the discriminating layer comprises apolyimide comprising groups of the Formula (1):


5. The composite membrane according to claim 1, wherein a portion of thegutter layer is present within the support and a portion of the gutterlayer is outside of the support and the following conditions aresatisfied: (i) the portion of the gutter layer outside of the supporthas an average thickness (GL_(e)) of 10 nm to 900 nm; and (ii) theportion of the gutter layer present within the support has an averagethickness (GL_(i)) of 10% to 350% of GL_(e).
 6. A gas separation modulecomprising a composite membrane according claim
 1. 7. The compositemembrane according to claim 1 wherein a portion of the gutter layer ispresent within the support and a portion of the gutter layer is outsideof the support and the following conditions are satisfied: (i) theportion of the gutter layer outside of the support has an averagethickness (GL_(e)) of 200 nm to 900 nm; and (ii) the portion of thegutter layer present within the support has an average thickness(GL_(i)) of 10% to 200% of GL_(e).
 8. The composite membrane accordingto claim 1 wherein a portion of the gutter layer is present within thesupport and a portion of the gutter layer is outside of the support andthe following conditions are satisfied: (i) the portion of the gutterlayer outside of the support has an average thickness (GL_(e)) of 400 nmto 900 nm; and (ii) the portion of the gutter layer present within thesupport has an average thickness (GL_(i)) of 20% to 90% of GL_(e). 9.The composite membrane according to claim 7 wherein the discriminatinglayer comprises a polyimide comprising trifluoromethyl groups.
 10. Thecomposite membrane according to claim 8 wherein the gutter layercomprises dialkylsiloxane groups.
 11. The composite membrane accordingto claim 1 wherein the gutter layer contains a metal and silicon in amolar ratio of at least 0.0005.
 12. The composite membrane according toclaim 1 which has a pure water permeability at 20° C. of less than6×10⁻⁸ m³/m²·s·kPa.
 13. The composite membrane according to claim 1which has a dry thickness of 20 to 500 μm.
 14. The composite membraneaccording to claim 10 which has a pure water permeability at 20° C. ofless than 6×10⁻⁸ m³/m²·s·kPa and a dry thickness of 20 to 500 μm.
 15. Agas separation module comprising a composite membrane according to claim8.
 16. A gas separation module comprising a composite membrane accordingto claim 14.